I'm often reading posts that claim a cable or individual audio component upgrade "transformed" a system. I always have to wonder what this means. Does it mean the system sounds different but not necessarily better? Or, does it mean a meaningful improvement but by how much? Plus how would your describe the gain? A percentage of overall SQ or some other metric. Stated another way this is a cost- benefit question. If we exclude speakers and room treatment which are universally agreed (?) upon as the most important components, what have been your most cost effective upgrade(s) in your system. Lets also specify this is a moderate to high-end system to begin with (50-100K).